Data errors in a disk drive recording apparatus such as a hard disk drive are largely divided into "hard" errors caused by a disk defect and "soft" errors caused by a bit shift. Generally, hard errors are prevented by designating an error position as a bad sector in an initial step; however, since the error position can not be designated for soft errors, soft errors are regarded as an important problem to be solved to ensure operational reliability for the disk drive recording apparatus.
Another fundamental problem of the hard disk drive is its weakness for physical impact and shock. Head gimbals, which support a head, should be flexible so that the head is separated from the surface of a disk by a minute gap, which is maintained as the disk rotates. Since the head gimbals are flexible, impacts or shocks upon the hard disk drive can cause errors when data is being read from the disk.
One invention aimed at reducing such errors is disclosed in U.S. Pat. No. 5,327,302 entitled Data Filter Tuning For Constant Density Recording Applications issued to Khoury et al. on 5 Jul. 1994. In Khoury et al. '302, a tunable data filter is altered so that the filter cutoff frequency is substantially proportional to a predetermined factor of an incoming data frequency, thereby creating a desired eye opening in the read data. While this invention has merit in its own respect, I believe it can be improved upon to even further reduce error rates of read data.